"Lasers again" distance measurement
On Fri, 2 Feb 2001 10:09:25 -0600, you wrote:
>Another way of measuring distance is to shoot a laser to a mirror( on a
>taget) and have the reflected beam 'interfere' with a ref beam. You can get
>very high resolutions. Basically counting the destructive/constructive waves
>of the laser.
Probably not much use for tractor-sized distances, but it does remind
me of a really fun demo...
Many He-Ne lasers have a rear mirror that lets some light pass (i.e.
not quite 100% reflective). Stick a photodiode to the back of this
mirror, and connect it to an audio amplifier and speaker.
Fire the laser at a mirror on the wall, and line it up so the beam
returns right back to the laser (i.e. beam at exactly 90 degrees to
the mirror on the wall)
You can now 'hear' any tiny movement of the wall via the speaker, e.g.
leaning on it, as it moves by a few hundred light wavelegths per
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In reply to: <005f01c08d32$83c23d00$740d53d1@robert>
See also: www.piclist.com/techref/displays.htm?key=laser
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